Antifriction coating formulation compositions

ABSTRACT

An antifriction coating formulation composition is disclosed. The antifriction coating formulation composition contains (a) a resin and (b) a metal sulfide containing molybdenum and cobalt, and optionally (c) a solid lubricant other than the metal sulfide and (d) a solvent. A coated film formed from the antifriction coating formulation composition provides better wear resistance as well as good coefficient of friction.

FIELD OF THE INVENTION

The present invention relates to antifriction coating formulationcompositions, antifriction coatings formed from the compositions, andsliding members having the antifriction coatings.

BACKGROUND OF THE INVENTION

Antifriction coatings are known in the art to improve sliding propertiesof components used for industrial machines, construction machines andautomobiles. Typical antifriction coating compositions comprise resinbinders, solid lubricants and solvents. Solid lubricants work to reducefriction and wear of contacting surfaces in relative motion and provideprotection from damage. Well-known solid lubricants include molybdenumdisulfide (MoS₂), graphite and polytetrafluoroethylene (PTFE).

Although antifriction coatings comprising molybdenum disulfide showexcellent sliding properties, it is always desirable to continue toimprove the wear properties. WO2016/073341A discloses a connecting rodcomprising a wear resistant coating. The wear resistant coatingcomprises a polymer matrix, solid lubricant and hard particles, whereinthe solid lubricant is selected from molybdenum disulfide, graphite,tungsten sulfide, hexagonal boron nitride, polytetrafluoroethylene andmetal sulfides. It can contain one or more solid lubricant. US7,368,182Bdiscloses a multiple coating layers to improve wear resistance.

Mixed-metal sulfides are known in the area of catalysis, such asWO2011/008513A and US4,752,623B. These prior art references disclosecobalt-molybdenum disulfide, in which small amount of cobalt metal isincorporated in the parent MoS₂ structure. In the use of catalyst, asecond metal (i.e. cobalt) incorporated into MoS₂ structure acts as acatalyst promoter. However, these prior art references do not mentionabout the use of the mixed metal sulfides as solid lubricants ofantifriction coatings.

SUMMARY OF THE INVENTION

Disclosed herein are an antifriction coating formulation compositioncomprising: (a) a resin and (b) a metal sulfide comprising molybdenumand cobalt, and optionally (c) solid lubricant other than the metalsulfide and (d) a solvent. Such antifriction coating formulationcomposition can provide an antifriction coating which exhibit higherwear resistance.

Also disclosed herein is a coated film formed from the antifrictioncoating formulation composition.

Further disclosed herein is a sliding member having a lubricating filmformed from the antifriction coating formulation composition.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a geometry of the test setup of ball-on-plate wear test.

FIG. 2 shows a geometry of LFW-1 (block on ring) test.

DETAILED DESCRIPTION OF THE INVENTION

The antifriction coating (AFC) formulation composition disclosed hereincomprises at least two ingredients: (a) a resin and (b) a metal sulfidecomprising molybdenum and cobalt, in which the molar ratio of molybdenumand cobalt in the metal sulfide is from 99 to 1 to 1 to 99.

Resin (a)

Resin (a) used in the antifriction coating formulation composition worksas a matrix polymer of a coating film described later. Examples of resininclude polyamideimide, polyimide, polyamide, epoxy resin, phenol resin,polybenzimidazole, polyphenyl sulfonate, polyether ether ketone,polyurethane, poly-butyltitanate, polyacryl-alkyd resin,polyetherketoneketone (PEKK), polyoxymethylene (POM), polybutyleneterephthalate (PBT), fluoropolymers, and mixtures thereof. Preferredresin includes polyamideimide, (polyimide) and (polyamide), withpolyamideimide most preferred.

Preferably, the resin present in the antifriction coating formulationcomposition ranges from 10 to 90 parts by weight with respect to 100parts by weight of the solid contents of the antifriction coatingformulation composition. More preferably, the resin content is from 20to 80 parts by weight, and even more preferably from 30 to 70 parts byweight, with respect to 100 parts by weight of the solid content of theantifriction coating formulation composition. In this specification, theweight of the solid contents of the antifriction coating formulationcomposition means the total weight of the solid contents of the AFCformulation composition (i.e., resin, metal sulfide, solid lubricant andadditional ingredients with solid form).

Metal Sulfide (b)

The metal sulfide used in the antifriction coating formulationcomposition comprises molybdenum and cobalt. Since the metal sulfidecomprises at least two metals, it is also called as mixed metal sulfide.When the metal elements of the metal sulfide are cobalt and molybdenum,the metal sulfide can also be called cobalt-molybdenum disulfide, andcan be described by the formula (Co,Mo)S₂ or Co_(x)Mo_((1-x))S₂. In theformula, x is a number less than 1.

The molar ratio of molybdenum and cobalt in the metal sulfide rangesfrom 99 to 1 to 1 to 99. The molar ratio can be selected based on therequired properties of the antifriction coating formulation compositioncomprising the metal sulfide. When the antifriction coating formulationcomposition comprising the metal sulfide is used for antifrictioncoatings with higher wear resistance, preferably the molar ratio ofmolybdenum and cobalt ranges from Mo:Co 85:15 to Mo:Co 98:2. In suchmolar ratio range, it is considered that a small amount of cobalt metalreplaces the molybdenum metal of the parent MoS₂ structure, so the wearresistance of a film comprising the metal sulfide is improved while thebasic antifriction property is maintained. More preferably, the ratio ofmolybdenum and cobalt in the metal sulfide is from Mo:Co 85:15 to 95:5,further more preferably, the ratio is from Mo:Co 90:10 to 95:5.

The metal sulfide can be obtained by the method described in thefollowing publications: 1) Cobalt-molybdenum sulfide catalysts preparedby in situ activation of bimetallic (Co—Mo) alkylthiomolybdates. Nava,et al, Catalysis Letters 2003, Vol. 86, No. 4, p. 257, and 2) The Roleof Structural Carbon in Transition Metal Sulfides HydrotreatingCatalysts. Berhault, et al. Journal of Catalysis 2001, Vol. 198 (1), pp.9-19.

The metal sulfide synthesized by this method produces a very dark solidwith a platelet structure, similar in appearance to MoS₂. The primaryparticle size of the metal sulfide tends to agglomerate in clusterspreferably from 0.1 to 10 micrometers, more preferably from 1 to 6micrometers. The size can be measured by a particle analyzer such aslaser diffraction scattering, or it can be estimated from ScanningElectron Microscope (SEM) images.

The amount of the metal sulfide in the resin composition ranges from 10to 60 parts by weight, preferably from 20 to 40 parts by weight, withrespect to 100 parts by weight of the solid content of the antifrictioncoating formulation.

Solid Lubricant (c)

The antifriction coating formulation composition can optionally comprisesolid lubricant (c). The solid lubricant is different from the metalsulfide (b) disclosed above. Non-limiting examples of solid lubricantsinclude graphite, polytetrafluoroethylene (PTFE), polyethylene (PE) andmixtures thereof. Graphite is preferable.

The solid lubricants in the antifriction coating formulation compositiondescribed herein are typically platelet-like in structure, with these“sheets” sliding relatively easily against each other. The materialsnaturally cluster into larger agglomerates that are easily broken downinto smaller particles during the preparation and mixing of theantifriction coatings. The average primary particle size of the solidlubricants is preferably from 0.1 to 10 micrometers, more preferablyfrom 1 to 6 micrometers.

When the antifriction coating formulation composition comprises a solidlubricant, the amount of the solid lubricant ranges from 1 to 100 partsby weight, preferably from 5 to 50 parts by weight and more preferablyfrom 10 to 30 parts by weight, with respect to 100 parts by weight ofthe solid content of the antifriction coating formulation composition.

Solvent (d)

The antifriction coating formulation composition can optionally comprisea solvent (d) for the purpose of improving coating properties. Thesolvent can be selected depending on the type of binder resin. Usablesolvents include, for example, ketones such as acetone, methyl ethylketone, methyl isobutyl ketone and cyclohexanone; esters such as methylacetate and ethyl acetate; aromatic hydrocarbons such as toluene andxylene; alcohols such as ethanol, 2-propanol, diacetone alcohol (DAA);organic halogen compounds such as methyl chloroform, trichloroethyleneand trichlorotrifluoroethane; N-methyl-2-pyrrolidone (NMP),N-ethyl-2-pyrrolidone (NEP), 1,3-dimethyl-2-imidazolidinone (DMI),3-methoxy-N,N-dimethylpropanemide, methylisopyrrolidone (MIP),dimethylformaldehyde (DMF), dimethylacetaldehyde (DMAC), and mixturesthereof. Preferred solvents are DMI, NEP and xylene.

Additional Ingredients (e)

The antifriction coating formulation composition described herein mayoptionally include additional ingredients such as a UV absorber, astabilizer, an antioxidant, a leveling agent, a deformer, a thickener, apigment, a dye and a dispersant as long as the object of the presentinvention is not impaired. When present, the amount of additionalingredients will preferably range from 0.1 to 5 parts by weight, withrespect to 100 parts by weight of the solid content of the antifrictioncoating formulation composition.

Although the metal sulfide (b) of the composition comprises cobalt andmolybdenum (Co_(x)Mo_((1-x))S₂), other metal sulfide (M_(x)Mo_((1-x))S₂,M is tungsten, tantalum or nickel) can be used.

The antifriction coating formulation compositions described herein maybe prepared using methods known to those skilled in the art, forexample, mixing the described ingredients using conventional apparatusin any suitable order. For example, dissolving resins and introducingthe metal sulfide and other ingredients if present.

Coated Film

The second aspect of the present invention relates to a coated filmformed from the above-mentioned antifriction coating formulationcomposition. The film is formed by applying the composition describedabove onto the surface of a substrate and then heating it to cure theapplied composition. The substrate can be metal, plastics, wood,elastomers, composites, etc. The coating can be applied to the surfaceby any conventional method, for example brushing, dipping and spraying.The coating thickness is determined from the required properties and thelife of the film, but it is typically from 5 to 20 micrometers. Once theantifriction coating formulation composition is applied on the surfaceof a substrate, it is dried to evaporate the solvent (if applicable) andis cured to form a coated film. The curing process depends on the natureof the substrate and the kind of resin. For example, the cure can beconducted in an oven for 30 to 90 minutes at a temperature of between100 to 280 degrees C.

Sliding Member

The third aspect of the present invention relates to a sliding memberhaving a lubricating film formed from the above-mentioned antifrictioncoating formulation composition. The sliding member can be selected froma swash plate of a compressor, an engine tappet, a camshaft, acrankshaft, an engine metal, an engine piston, an engine fastener, aslide bearing, a piston ring, a gear, a door lock, a brake shim or abrake clip.

Examples Examples Series I: Wear Resistance Tests

The raw materials shown in Table 1 were used to prepare compositions inthe Examples.

TABLE 1 Material Product names and Type Description properties SupplierA-1 Polyamide imide resin DMI-soluble — polyamide imide A-2 Polyamideimide resin NEP-soluble — polyamide imide B-1 MoS₂ 0.1-10 Climaxmicrometers of Molybdenum median diameter Company B-2 Co_(x)Mo(_(1−x))S₂(x = 0.01) — — B-3 Co_(x)Mo(_(1−x))S₂ (x = 0.05) — — B-4Co_(x)Mo(_(1−x))S₂ (x = 0.10) — — B-5 Co_(x)Mo(_(1−x))S₂ (x = 0.20) — —B-6 Co_(x)Mo(_(1−x))S₂ (x = 0.33) — — B-7 Co_(x)Mo(_(1−x))S₂ (x = 0.50)— — B-8 Co_(x)Mo(_(1−x))S₂ (x = 0.125) C-1 Graphite Graphite powderGraphite with 0.1-10 Kropfmuehl micrometers of GmbH median diameter C-2PTFE PTFE powder with Central Glass 5-7 micrometers Co., Ltd. of mediandiameter D-1 DMI 1,3-dimethyl-2- Mitsui imidazolidinone Chemicals, Inc.D-2 NEP N-ethyl-2- Sankyo pyrrolidone Chemical Co., Ltd. D-3 xylene —E-1 Ethyl methyl siloxane, 2- Defoamer Dow Chemical phenyl propyl methylRefractive index siloxane copolymer 1.46 Kinematic viscosity 1400 cSt

Preparation of Co_(x)Mo_((1-x))S₂

Stoichiometric amounts of ammonium sulfide [(NH₄)₂S] and ammoniumheptamolybdate [(NH₄)₂Mo₇O₂₄-4H₂O] were combined in water solution andstirred at 60° C. for 1 hour (during which solids will completelydissolve). The resulting water solution was co-dripped with thestoichiometric amount of a water solution of cobalt acetate[Co(C₂H₃O₂)₂] from an addition funnel into an acetic acid solution at60° C. and allowed to stir for one hour. The resulting solid material{(NH₄)₄[Co(MoS₄)₃]} was filtered and dried at 80° C. The dry materialwas then placed into a purged nitrogen furnace, ramped up to 500° C.,and held for about one hour to reduce the solid to the final sulfideproduct. After heating the furnace was allowed to cool down naturallywhile remaining under nitrogen atmosphere.

Characterization of Co_(x)Mo_((1-x))S₂

As synthesized, Co_(x)Mo_((1-x))S₂ show the same phases by powder X-raydiffraction as those present in the parent MoS₂ structure; however, thepeaks are weaker and broader because of a nanocrystalline structure. Byscanning electron microscopy/electron dispersive spectroscopy (SEM-EDS),the cobalt is relatively evenly distributed over the grains, andparticle sizes are estimated at roughly 2 microns or less. These appearto be clusters of a smaller primary particle size on the order of 100 sof nm, and some large agglomerates are also present. It is likely thatthe large agglomerates are broken up in the antifriction coatingformulation during the milling process.

Mixed metal sulfide were analyzed by X-ray fluorescence to get truestoichiometric ratios of Co:Mo. Data in examples are shown as roundedratios for simplicity.

Test Methods

Test 1: Ball-On—Plate Wear Test

Ball-on-plate wear test was conducted following ASTM G-133. A ½″diameter steel ball (11) was brought into contact with the anti-frictioncoating (21), which has been applied to a steel (or other material)coupon, with a force of 10N. The load was maintained throughout the testas the test sample was reciprocated back and forth with a stroke lengthof 4 mm for a total of 10,000 passes (or 5000 cycles). The geometry ofthe test setup (1) from ASTM G-133 is shown in FIG. 1 for reference.

Test 2: LFW-1 Test

LFW-1 test is another wear test frequently conducted on antifrictioncoatings, which follows ASTM-D 2714. This dry test is done at relativelyhigh load (2860N), at 72 rpm for the coated test ring (Rockwell hardness60); geometry is an upper block applying the load on the ring spinningon a shaft underneath. See FIG. 2 for the wear test geometry schematics.

EXAMPLES

Antifriction coating formulation compositions disclosed in Tables 2 and3 were prepared and tested. Ingredients (resin, MoS₂ orCo_(x)Mo_((1-x))S₂, solid lubricant, solvent and additive) were mixed bymilling and subsequent filtration, then sprayed onto a substrate to maketest films. The test films were heated at 80 degrees C. for 10 minutes,followed by 230 degrees C. for 1 hour, in order to cure the resin.

TABLE 2 Samples 1 2 3 4 5 6 7 A-1 100.00 100.00 100.00 100.00 100.00100.00 100.00 A-2 0 0 0 0 0 0 0 C-1 8.01 8.01 8.01 8.01 8.01 8.01 12.67C-2 0 0 0 0 0 0 0 B-1 0 0 51.28 0 0 0 0 B-2 0 0 0 51.28 0 0 0 B-3 51.280 0 0 0 0 0 B-4 0 51.28 0 0 0 0 0 B-5 0 0 0 0 51.28 0 0 B-6 0 0 0 0 051.28 0 B-7 0 0 0 0 0 0 81.60 D-1 0 0 0 0 0 0 0 D-2 316.67 316.67 316.67316.67 316.67 316.67 733.18 D-3 0 0 0 0 0 0 0 E-1 0.62 0.62 0.62 0.620.62 0.62 0.93 Total 476.58 476.58 476.58 476.58 476.58 476.58 928.38Ave 0.16 0.138 0.214 0.153 0.208 0.184 0.16 CoF Table 28 18 36 100 77 3752 Wear Scur Depth (%)

TABLE 3 Samples 8 9 10 11 A-1 0 0 0 0 A-2 100.00 100.00 100.00 100.00C-1 0 0 0 0 C-2 22.25 22.25 22.25 22.25 B-1 0 0 0 68.09 B-2 0 0 0 0 B-368.09 0 0 0 B-4 0 68.09 0 0 B-8 0 0 68.09 0 C-2 28.34 28.34 28.34 28.34D-1 248.86 248.86 248.86 248.86 D-2 0 0 0 0 D-3 69.28 69.28 69.28 69.28E-1 0 0 0 0 Total 536.82 536.82 536.82 536.82 LFW-1 R-1 146,651 144,236144,236 68,000 test, Cycle R-2 178,934 142,984 142,984 number at Ave162,793 143,610 143,610 seizure Oscillation Wear Scar 53 69 test Depth(%) at 15K Cycle number 96,700 41,600 at seizure

Examples Series II: Wear Life Tests

Using the formulation of Samples 8 and 11, long term ball-on-plate testswere conducted. The film thickness of Samples 8 and 11 were 13.7 and11.0 micrometers respectively. The formulation with the Sample 8 lastsmuch longer before failure than Sample 11. Control samples of Sample 11were tested in winter and in summer in order to ensure that there wasnot a significant influence from large changes in relative humidity.

TABLE 4 Wear scar Cycles Aver- depth Aver- Specific (if no age Cycles %(microm- age Samples condition fail) CoF to fail wear eters) S:Mo 11  5K0.14 — 63 6.9 1.39 10K 0.14 — 70 7.7 1.29 15K 0.14 — 69 7.6 1.35 25K0.14 — 76 8.4 1.58 35K 0.17 — 80 8.8 Sulfate only Summer — — 41.6K 829.1 3.17 Summer — — 41.6K 89 9.8 Sulfate only Winter — —   44K — — 8  5K0.14 — 68 9.3 1.30 10K 0.15 — 58 7.9 1.35 15K 0.16 — 53 7.3 1.39 — —96.7K 51 7.0 1.81 170K  0.16 — 74 10.2 1.99

S:Mo ratios are also shown in Table 4. Using X-ray photoelectronspectroscopy, the ratios of sulfur to molybdenum were calculated fromthe peaks corresponding to the relevant bonding states and are correctedfor relative sensitivity. These estimates are reasonable, as indicatedby the values on the film surfaces of 1.94 (Sample 11) and 1.93 (Sample8). The Sample 11 containing standard MoS₂ indicates with all of thesamples with high wear times or failure that the sulfur is present assulfate, not sulfide. This is a key difference from the Sample 8 withmixed metal sulfide, as the sulfide:Mo ratios remain quite similar tothe original film surface values. While it is still not completelyunderstood, this difference does support the idea that the presence ofthe cobalt in the MoS₂ structure could possibly delay or inhibit theoxidation that correlates with wear.

1. An antifriction coating formulation composition comprising: (a) aresin and (b) a metal sulfide comprising molybdenum and cobalt, whereinthe molar ratio of molybdenum and cobalt in the metal sulfide is from 99to 1 to 1 to
 99. 2. The antifriction coating formulation composition ofclaim 1, wherein the amount of the metal sulfide is from 10 to 60 partsby weight, with respect to 100 parts by weight of the solid contents ofthe antifriction coating formulation composition.
 3. The antifrictioncoating formulation composition of claim 1, wherein the average particlesize of the metal sulfide is from 0.1 to 10 micrometers observed byScanning Electron Microscope.
 4. The antifriction coating formulationcomposition of claim 1, further comprising at least one (c) solidlubricant other than the metal sulfide.
 5. The antifriction coatingformulation composition of claim 4, wherein the solid lubricant isselected from graphite, polytetrafluoroethylene and polyethylene.
 6. Theantifriction coating formulation composition of claim 1, furthercomprising (d) a solvent.
 7. The antifriction coating formulationcomposition of claim 1, wherein the resin is selected frompolyamideimide, polyimide, polyamide, epoxy resin, phenol resin,polybenzimidazole, polyphenyl sulfonate, polyether ether ketone,polyurethane, poly-butyltitanate, polyacryl-alkyd resin, polyetherketone ketone, polyoxymethylene, polybutylene terephthalate, orfluoropolymers.
 8. The antifriction coating formulation composition ofclaim 1, wherein the ratio of molybdenum and cobalt in the metal sulfideis from 85 to 15 to 95 to
 5. 9. A coated film formed from theantifriction coating formulation composition of claim
 1. 10. The coatedfilm of claim 9, wherein the film is formed on a metal surface of acomponent.
 11. A sliding member having a lubricating film formed fromthe antifriction coating formulation composition of claim
 1. 12. Thesliding member of claim 11, wherein the sliding member is selected froma swash plate of a compressor, an engine tappet, a camshaft, acrankshaft, an engine metal, an engine piston, an engine fastener, aslide bearing, a piston ring, a gear, a door lock, a brake shim and abrake clip.